Extensions.conf

Adapted from Asterisk config extensions.conf - voip-info.org. You are encouraged to read the original first as some material is omitted  to simplify presentation. Attempt was made to reformulate the concepts in term of subroutines, which are probably more understandable to programmers who get used to languages such as C, Java, Perl, etc.

• Context Inclusion
• Extensions
• Predefined Extension Names
• Defining Extensions
  • Example
• Variables and expressions
• Reloading
• One big file or several small?
• Forwarding to another Asterisk
• Controlling extensions.conf from outside
• Macro Examples
• Sip header manipulation examples
• Example files on the net

The configuration file "extensions.conf" contains so called "dial plan" of Asterisk. This is ad hoc scripting language that provides idiosyncratic (pretty obscure) way of  specifying control flow and operations of Asterisk PBX.  Program in this language specified in extensions.conf  controls how incoming and outgoing calls are handled and routed.  In version 1.6 dialplan can be programmed in Lua which I highly recommend ( see lua.sample ). It requires a new module that was developed by Matt Nicholson of Digium

The content of "extensions.conf" is organized in sections, which can be either for static settings and definitions, or for executable dialplan components in which case they are referred to as Asterisk context.

• General The first two  sections are general
• Globals
• User defined Contexts.  Sections (contexts) are similar to classes in C++ or Java and contan set of "methods" -- extensions defined for the given context to which asterisk will connect. That provides separation of extension namespaces in "chunks" which is important for security reasons.
  • A special subclass of user-defined contexts are macros They should have a name prefixed with macro-. These are reusable execution patterns, like procedures in a programming language.

Every user-defined context section in extensions.conf starts with the name of the section contained within square brackets somewhat similar to Windows .ini file format.  Simplifying we can view context as a group of extensions. Only those extensions that exist in particular context can be dialed from the channel that uses it  (channels are defined in sip.conf and can be viewed as devices connected to you VIOP network. In other words each extension exists within a particular context.

Tip:

• Use vim or other editor with syntax highlighting for editing,  vim syntax highlighting  can prevent some errors or typos.
• For tips for debugging dialplan see Dialplan debugging

[general]

• At the top of your extensions.conf file there is a section named [general] where you can configure a few general settings . For details, see: Dialplan General Settings

• In this section, you may define global variables (or constants) and their initial values. For details, see:
  • Dialplan Global Variables
  • Using Variables in Asterisk Dialplans

• After the [general] and [globals] categories, the remainder of the extensions.conf file is taken up by the definition of the Dialplan. The Dialplan consists of a collection of contexts. Each context consists of a collection of extensions. For an introduction to these topics, see:
  • Introducing Contexts and Extensions
• When you define the extensions within a context, you may not only use literal numbers, not only alphanumeric names, but also you may define extensions that match whole sets of dialed numbers by using extension patterns. For more information about this, see:
  • Extension Names and Patterns

Context Inclusion

Context "default":
Extension Description
101 Mark Spencer
102 Wil Meadows
0 Operator

Context "local":
Extension Description
_9NXXXXXX Local calls
include => "default"

Context "longdistance":
Extension Description
_91NXXNXXXXXX Long distance calls
include => "local"

Here we have defined three extensions:

• The context default permits dialing three telephone extensions: Mark, Wil, and the Operator.
• The context local has one extension pattern to permit dialing 7-digit numbers only (local calls), and also includes the context "default", thus also permitting a user to dial Mark, Wil, or the Operator.
• The context long distance has one extension pattern to permit dialing a long-distance call, and it also includes the context "local", thus permitting the user to make local calls and also to dial the extensions of Mark, Wil or the Operator.

If more than one pattern matches a dialed number, Asterisk may not use the one you expect. See Sort Order of Extension Patterns.

Adding to an existing section (I believe this is a 1.4 feature; additional info on similar option are in doc/configuration.txt of asterisk src tree)

[section]
label = value

[section](+)
label2 = value2

In this case, the plus sign indicates that the second section (with the same name) is an addition to the first section. The second section can be in another file (by using the #include statement). If the section name referred to before the plus is missing, the configuration will fail to load.

When Asterisk receives an incoming connection on a channel, Asterisk call the subroutune -- the context defined for that channel. This subroutine contains set of extension that are availble for anybody who dial this channel.

In turn the context consists of several subroutines, each defining one or multipole extentions.

For some kinds of connections - such incoming calls from an outside telephone line - the user has not dialed an extension. In that case, Asterisk behaves as if the user had dialed a special extension named "s" (for Start). Asterisk will look for an extension "number" s in the definition of the context for that channel for instructions about what it should do to handle the call.

Let's say, for example, that you have a channel "Incoming" which is a connection from your VOIP provider. The condfigation file for SIP channels is sip.conf. In it you need to define context=incoming. So when you call from your cell phone this number, Asterisk will lookup the context with the name "incoming" in extensions.conf to find out what it should do with the call:

[incoming]

Within this context Asterisk will try to find subroutine that corresponds to the extention dialed.

This subroutine connects the call with the other phone or mailbox and/or perform additional actions on the call It usually ends the command Handup.

• literal. A literal extension can be a number, like 123. It can also include two special symbols * and # that appear on keypad of telephones, so 12# and *89 are valid extensions. Asterisk uses several predefined extension:
  • i : Invalid
  • s : Start
  • h : Hangup
  • t : Timeout
  • T : AbsoluteTimeout
  • a : Asterisk extension
  • o : Operator

See Asterisk standard extensions for details.

Extention definition in Asterisk is a subroutine which specifies set of commands to execute. Like in eary Fortran command are generally executed in the order defined by their labels called "priority" tag. Some commands, such as the Dial and GotoIf commands, have the ability to redirect somewhere else, based on some condition.

• Patterns. We will discuss then later.

When an extension is dialed, the command tagged with a priority of 1 is executed, followed by command priority 2, and so on. This goes on until:

• the call is hung up,
• a command returns a result code of -1 (indicating failure).
• a command with the next higher priority doesn't exist (note: Asterisk will not "skip over" missing priorities)
• the call is routed to a new extension.

exten = extension,priority,Command(parameters)

where the equal sign can also be ornamented as an arrow, i.e., "=>", a form most often seen in many examples.
The components of an extension execution step or command line are the following:

• extension is the label of the extension, and can be either a literal constant string (alphanumeric plus a few special symols allowed) or a dynamically evaluated pattern (see below) to match many possible phone numbers, for example. Every command line that is part of a given extensions has this same label.
  
• priority is usually an integer (see note, however). It's just a sequence number for each command line of an extension. The first executable command of an extensions has the priority "1", so when Asterisk transfers a call to an extension, it will look for a command with priority 1. If there is not a line with a priority of 1, then the extension will not match the dialed number. After executing the priority 1 command, Asterisk will increment the priority to "2" unless the command itself determines the next priority to be executed. If this next priority is not defined in the extension, Asterisk finishes processing for this extension, even if there exists another command with a priority higher than the missing one.

Note: Auto increment n can be used instead of numeric priorities other then 1 (see Asterisk standard extensions), for example:

exten => 123,1,Answer
exten => 123,n,Playback(welcome)
exten => 123,n,Voicemail(44)
exten => 123,n,Hangup

This is the definition of a single extension with name "123". When a call is made to extension 123, Asterisk will answer the call itself, play a sound file called "welcome", give the user an opportunity to leave a voicemail message for mailbox 44, and then hang-up.

Other options for defining extensions include an option commonly referred to as the ex-girlfriend logic. This logic will match the dialed extension, whether it came from outside or inside, based on the callerid of the person calling it. For example:

exten => 123/100,1,Answer()
exten => 123/100,2,Playback(tt-weasels)
exten => 123/100,3,Voicemail(123)
exten => 123/100,4,Hangup()

This will match extension 123 and perform the following options ONLY if the Caller-ID Number of the calling user is 100. This can also be accomplished with pattern matching, as seen below:

exten => 1234/_256NXXXXXX,1,Answer()
and so on...

This will only match for 1234 if the Caller ID Number is something beginning with 256. This is very useful to keep locals from dialing your toll-free number and charging you for the call.

You can even do this:

exten => s,1,Answer
exten => s/9184238080,2,Set(CALLERID(name)=EVIL BASTARD)
exten => s,2,Set(CALLERID(name)=Good Person)
exten => s,3,Dial(SIP/goodperson)

Basically the call comes in, at 2 you change callerID for the people you don't like out, everybody else stays in the path and at 3 everybody is back in the main path.

Syntax for defining a context: keywords exten, include, ignorepat and switch.

• How Does Asterisk Handle "Match As You Go" Dialing?

Reloading

Either connect to your asterisk process with asterisk -r or rasterisk and type in the command, or send the command directly with:

asterisk -rx 'dialplan reload'

Macro Examples

[macro-oneline]
exten => s,1,Dial(${ARG1},20,t)
exten => s,2,Voicemail(u${MACRO_EXTEN})
exten => s,3,Hangup
exten => s,102,Voicemail(b${MACRO_EXTEN})
exten => s,103,Hangup

[local]
exten => 6601,1,Macro(oneline,${PHONE1})
exten => 6602,1,Macro(oneline,${PHONE2})

• Asterisk dial plan - working example: Real world example
• An expanded example showing integrations with a Panasonic KSU ivr

NEWS CONTENTS

• 200102 : Asterisk config extensions.conf - voip-info.org ( Asterisk config extensions.conf - voip-info.org, )

Old News

Asterisk config extensions.conf - voip-info.org

Hi
I need to add a line which will let callers to enter * if they have made a mistake entering the extension.

for example if they have entered 123 and they want to clear it all and enter 1245

Re: Extentions

It's pretty simple to manipulate sip extensions with Asterisk. I see no one answered this so here's the soluion...

; --- user dials 9+ and we manipulate dialled digits ---

; --- just wait two seconds before dialling the extension ---
exten => _9.,1,Wait(2)

; --- prefix + and strip off user dialled 9 then place call for two seconds ---
exten => _9.,n,Dial(SIP/+${EXTEN:1}@sipcarrier,2)

; --- prefix + and strip off user dialled 9 then place call to othersipcarrier ---
exten => _9.,n,Dial(SIP/+${EXTEN:1}@othersipcarrier)

Recommended Links

• Asterisk Dialplan Planning
• Using Variables in Asterisk Dialplans
• Using Functions in Asterisk Dialplans
• vim syntax highlighting for extensions.conf
• Extension Names and Patterns
• Sort Order of Extension Patterns
• Dialplan Commands
• The Asterisk handbook (draft) includes a good explanation and many examples
• Asterisk config sip.conf: sip.conf sample configurations
• Asterisk - dual servers: How to connect to an extension in another Asterisk server over IAX.
• Asterisk tips and tricks
• Asterisk howto dial plan: How to build a dial plan
• International numbering plans and phone number analysis
• Dialplan Renumberer Utility - Beta resource for renumbering your dialplan if you have to insert/delete a priority.
• Asterisk Dialplanner - A Java-based point-and-click web tool to help you create your dialplan.
• radp - Ruby Asterisk Dial Plan generator (create your dialplans with ruby)
• http://www.astautodialer.com - AstPlanDesigner (part of AstAutoDialer) - A graphical tool to draw and visualize your Asterisk dial plan!
• Asterisk Configuration files

  Examples

  • John Todd, Loligo.com: http://www.loligo.com/asterisk/current/extensions.conf
  • Tilghman Lesher: http://asterisk.drunkcoder.com/extensions.conf
  • planetWayne: Ideas for Home Based Asterisk Systems

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Last modified: March 12, 2019